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The double Fourier transform of non-Lebesgue integrable functions of bounded Hardy–Krause variation

  • Francisco J. Mendoza EMAIL logo , Juan H. Arredondo , Salvador Sánchez-Perales , Oswaldo Flores-Medina and Edgar Torres-Teutle
Published/Copyright: April 6, 2023
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Abstract

In the classical Fourier analysis, the representation of the double Fourier transform as the integral of f ( x , y ) exp ( i ( x , y ) , ( s 1 , s 2 ) is usually defined from the Lebesgue integral. Using an improper Kurzweil–Henstock integral, we obtain a similar representation of the Fourier transform of non-Lebesgue integrable functions on R 2 . We prove the Riemann–Lebesgue lemma and the pointwise continuity for the classical Fourier transform on a subspace of non-Lebesgue integrable functions which is characterized by the bounded variation functions in the sense of Hardy–Krause. Moreover, we generalize some properties of the classical Fourier transform defined on L p ( R 2 ) , where 1 < p 2 , yielding a generalization of the results obtained by E. Hewitt and K. A. Ross. With our integral, we define the space of integrable functions KP ( R 2 ) which contains a subspace whose completion is isometrically isomorphic to the space of integrable distributions on the plane as defined by E. Talvila [The continuous primitive integral in the plane, Real Anal. Exchange 45 (2020), 2, 283–326]. A question arises about the dual space of the new space KP ( R 2 ) .

MSC 2010: 42C10; 46B07

Funding statement: This research was supported partially by CONACyT-SNI, Mexico.

Acknowledgements

The authors express their sincere gratitude to Nancy Keranen for her selfless assistance. They thank the referees for their valuable comments and suggestions which help improve this paper.

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Received: 2022-03-05
Revised: 2022-10-16
Accepted: 2022-10-27
Published Online: 2023-04-06
Published in Print: 2023-06-01

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